1. Nanostructured and Organic Optical and Electronic Materials, Department of Physics, University of Antwerp, B-2610 Antwerp, Belgium
2. Institute of Nanotechnology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
3. Materials Science and Engineering Division, National Institute of Standards and Technology, 20899 Gaithersburg, Maryland, United States
4. Faculty of Physics, University of Sofia, BG-1164 Sofia, Bulgaria
5. Laboratoire des Multimatériaux et Interfaces, UMR CNRS 5615, Univ Lyon, Université Claude Bernard Lyon 1, F-69622 Villeurbanne, France
6. CIRIMAT, UMR 5085, CNRS-INP-UPS, Université Toulouse 3 Paul Sabatier, 118 route de Narbonne, F-31062 Toulouse cedex 9, France